Question - will they even be allowing people other than "trade negotiators and corporate lobbyists" and the like to attend?

Moving the location would only make sense as an evasion tactic if outside parties are even a factor in the first place. If the only people in attendance are going to be insiders anyway, then it hardly matters where they hold it.

I'd guess they're trying to avoid protesters setting up outside the meeting. They are already getting some negative attention, and I'd expect they would want to prevent attracting more bad press on short timescales.

My understanding is that it's considered insensitive to subject important people to the sight of the unwashed masses who hate them, or even the perimeter of riot pigs and razor wire that it takes to keep their meeting undisturbed.

Keeping the meeting undisturbed is considered a minimum condition, which is why host cities do roll out the big guns for the occasion; but nobody likes to be reminded of how much effort is required to keep their bubble of comfortable and shared assumptions isolated.

Consider the example of the ongoing epic butthurt of the American plutocracy: despite having basically all their economic demands met or exceeded, you've got people crying about how not being respected and praised in all corners is just a step or two away from being herded into the gas chambers.

We can only hope that the security gets so overblown that people who are supposed to be in meetings don't know where they're being held, and agreements don't get made or they're made multiple times with mutually contradictory clauses.

Meanwhile, I'm sure that Ottawa can rustle up some local protestors. How many venues in Ottawa could host such a secure, high-level meeting?

As a non-biassed Brit (!), can someone please explain to me how a "trade agreement" can somehow become a legal entity (unless I'm reading everything wrongly) without going through, or being ruled on by a court of law? Are there some new rules about companies now being able to make up their own laws and rules as they go along? What legal basis does this TPP have in the real world?

Question - will they even be allowing people other than "trade negotiators and corporate lobbyists" and the like to attend?

You're right that no one can attend but it's way more annoying than that. At negotiating rounds TPP opponents, who aren't allowed at the actual negotiations, often hold events in the city (talks, workshops, etc) and invite the delegates to them. A surprisingly large amount of them actually attend (often if there's a lunch involved as we all know how bad conference food is).

Moving it at a late stage like this disrupts all the plans of the opponents as they scramble to find new venues and new accommodation. Moreover, moving it further away from the Pacific (the second P in TPP) means opponents from countries like (for example) New Zealand, can see their airfare costs go way way up.

It's also not the first time this has happened. Last year talks were held in Japan but no details emerged of where or when until it was too late to plan anything. In Brunei as well, dates, times and locations were all changed at the last minute meaning opponents were often left (almost) literally scrambling from place to place.

Full disclosure: I'm part of the Fair Deal network (Consumer NZ) and spoke at the Brunei round of negotiations last year.